a. Field of Invention
The invention relates generally to intake and exhaust systems for engines, and, more particularly to an intake and exhaust system for a dual mode HCCI engine, which provides superior intake temperature and pressure control for engine operation in SI and HCCI modes.
b. Description of Related Art
Compared to conventional engines, homogeneous charge compression ignition (HCCI) engines potentially have high efficiency, very low emissions of oxides of nitrogen (NOx) and particulates, and relatively low cost. HCCI engines however must operate over the same operating range, in terms of speed and torque, as conventional SI or diesel engines. Because HCCI is limited by harsh combustion at higher torques, it is common for the engine to employ both SI and HCCI combustion mode technology. At medium torque, the engine can operate in HCCI mode to achieve high fuel efficiency and low NOx emissions. At higher torques however, combustion mode of the engine may be switched to SI mode.
For an HCCI engine with a limited compression ratio, the intake temperature in HCCI mode should preferably be high enough for auto-ignition. In other words, the lower the torque, the higher the intake temperature should preferably be. The air-fuel mixture for a dual combustion engine in HCCI mode is diluted by air or by exhaust gas recirculation (EGR) through the use of high intake pressure (i.e. unthrottled operation at medium torque) to suppress NOx formation. In contrast, the intake temperature of a dual combustion engine in SI mode should preferably be low enough (i.e. close to the ambient temperature) to avoid knocking, and the air-fuel mixture should preferably be at, or close to, stoichiometric. Thus, when a dual combustion engine is switching from HCCI mode to SI mode, the inlet temperature should preferably decrease quickly and the intake pressure should preferably also decrease quickly to restrict the intake airflow to form a stoichiometric mixture at a medium torque.
A good control of the intake pressure can also improve dual combustion engine performance under some special conditions. At idle, when the dual combustion engine is operating in HCCI mode, the engine may be throttled to control the air-fuel ratios to below 80:1, which can increase the exhaust gas temperatures and reduce CO emissions. At the high-torque boundary of the HCCI operating region, boosting the intake pressure can dilute the mixture to reduce NOx emissions and to control the combustion rate, thus expanding the HCCI region to higher torques. In SI mode, boosting the intake pressure at high torques can provide higher torque output. This feature is especially important if the dual combustion engine has a fixed geometric compression ratio higher than those for conventional SI engines. This is because boosting the intake pressure can compensate the loss in volumetric efficiency, due to the reduced effective compression ratio (for avoiding knock). In SI mode, the compressed intake air should preferably be cooled down by an intercooler to control engine knock. In contrast, cooling the compressed intake air is not necessary during the HCCI mode.
Accordingly, the intake/exhaust system for a dual-mode HCCI engine can be relatively complicated, as evidenced by the aforementioned description.
Various related-art intake/exhaust systems for HCCI engines are known and disclosed, for example, in U.S. Pat. No. 6,295,973 to Yang (Yang), and SAE paper Nos. 2001-01-1031, 2001-01-1896 and No. 2001-01-1897.
U.S. Pat. No. 6,295,973 to Yang, the disclosure of which is incorporated herein by reference, discloses an intake system for an HCCI engine, which proposes using the waste thermal energy in the coolant and exhaust gases to heat the intake air and control the intake air temperature by mixing the heated and un-heated air streams with different mass ratios of the two air streams. Additionally, SAE paper Nos. 2001-01-1031, 2001-01-1896 and No. 2001-01-1897 disclose an HCCI engine intake system with a turbocharger, an intercooler, and heaters, and HCCI engine intake systems with supercharging or turbo These related-art references however do not provide fast intake temperature and pressure control for SI and HCCI operations of a dual-mode HCCI engine.
Accordingly, there remains a need for an intake and exhaust system for a dual-mode HCCI engine, which achieves fast intake temperature and pressure control for engine operation in both the SI and the HCCI modes, which is structurally and economically feasible to manufacture and install, and which efficiently and reliably achieves the required temperature and pressure characteristics for the relatively complicated operation of the dual-mode HCCI engine.
The invention solves the problems and overcomes the drawbacks and deficiencies of prior art intake and exhaust systems by providing a novel method and apparatus for controlling intake air temperature and pressure in a dual-mode HCCI engine.
Thus, an aspect of the present invention is to provide fast control of the intake air temperature and pressure incorporated with intake pressure boosting.
Another aspect of the present invention is to provide an intake/exhaust system and control method thereof for allowing quick variation of the intake air temperature and intake air pressure, while allowing boosting of the air temperature and pressure above ambient conditions.
Specifically, the invention provides an intake/exhaust system for a dual-mode homogeneous charge compression ignition (HCCI) engine having intake and exhaust manifolds. The system may include an air compressor for boosting intake pressure of air supplied to the engine and including at least two output air flow paths. The system may further include an intercooler for cooling air from a first one of the air flow paths, at least one heat exchanger for heating air from a second one of the air flow paths, and control valves for controlling the mass ratio of air through the air flow paths to thereby control temperature and pressure of air supplied to the engine. In this manner, the first air flow path may direct air to the engine via the intercooler and the second air flow path may direct air to the engine via the heat exchanger, such that air at a first temperature is supplied to the engine for operation in SI mode and air at a second temperature is supplied to the engine for operation in HCCI mode.
For the system described above, the air compressor may be a supercharger, an E-booster (i.e., air compressor driven by an electric motor), or a turbocharger. For the supercharger, a pressure release valve operable to control pressure downstream of the supercharger may be provided. For the E-booster, a bypass valve operable to control pressure downstream of the E-booster may be provided. The bypass valve may be closed upon activation of the E-booster and open upon deactivation of the E-booster. A catalyst may be disposed between the engine exhaust manifold and one of the heat exchangers. For the turbocharger, an exhaust bypass valve may be provided, located downstream of the turbocharger, operable in conjunction with an intake bypass valve, located upstream of the turbocharger, for controlling operation of the turbocharger. An exhaust gas recirculation (EGR) line may be provided for directing exhaust gas from an exhaust heat exchanger to the air compressor, and may include an EGR control valve for controlling the flow of exhaust gas through the EGR line.
The invention also provides an intake/exhaust system for a dual-mode homogeneous charge compression ignition (HCCI) engine including intake and exhaust manifolds. The system may include an air compressor for boosting intake pressure of air supplied to the engine and include at least two output air flow paths. The system may further include an intercooler for cooling air from a first one of the air flow paths, at least one heat exchanger for heating air from a second one of the air flow paths, and a throttle for controlling flow of air from the intercooler to engine cylinders. In this manner, the first air flow path may direct air to the engine via the intercooler and the second air flow path may direct air to the engine via the heat exchanger, such that air at a first temperature is supplied to the engine for operation in SI mode and air at a second temperature is supplied to the engine for operation in HCCI mode.
For the system described above, three-way control valves may be provided for controlling the mass ratio of air through the throttle to thereby control temperature and pressure of air supplied to the engine. Each of the three way valves may include two input air flow paths and one output air flow path for supplying air to the engine. One of the input air flow paths may receive air controlled by the throttle, the other one of the input air flow paths may receive air from the heat exchanger.
Alternatively, for an engine including at least two intake valves and at least one exhaust valve, the system may include at least one variable valve timing device for controlling at least one of the intake valves to control the mass ratio of air supplied to the intake valves to thereby control temperature and pressure of air supplied to the engine. A first variable valve timing device may control a first intake valve, thereby controlling the supply of air through the throttle to the first intake valve. A second variable valve timing device may control a second intake valve, thereby controlling the supply of air through the heat exchanger to the second intake valve. Alternatively, the system may include at least one port throttle for controlling air flow to at least one of the intake valves to control the mass ratio of air supplied to the intake valves to thereby control temperature and pressure of air supplied to the engine. A first port throttle may control air flow to a first intake valve, thereby controlling the supply of air through the throttle to the first intake valve. A second port throttle may control air flow to a second intake valve, thereby controlling the supply of air through the heat exchanger to the second intake valve.
In another configuration, the system may include at least one additional throttle for controlling air flow to each of the intake valves to control the mass ratio of air supplied to the intake valves to thereby control temperature and pressure of air supplied to the engine. The additional throttle may control air flow through the second air flow path. Thereafter, air within the first and second air flow paths may be mixed and supplied to the intake valves. Alternatively, the additional throttle may control air flow to one of the intake valves to control air supplied to the intake valve and to thereby control temperature and pressure of air supplied to the engine. The additional throttle may control air flow through the second air flow path. Thereafter, air within the first air flow path may be directly supplied to another one of the intake valves.
The invention further provides a method of controlling intake air temperature and pressure in a dual-mode homogeneous charge compression ignition (HCCI) engine having intake and exhaust manifolds. The method may include supplying air to the engine via at least two air flow paths, cooling air in one of the air flow paths and heating air in another one of the air flow paths. The method may further include controlling the mass ratio of air through the air flow paths to thereby control temperature and pressure of air supplied to the engine, and boosting intake pressure of air supplied to the engine. In this manner, air at a first temperature may be supplied to the engine for operation SI mode and air at a second temperature may be supplied to the engine for operation in HCCI mode.
The method described above may further include utilizing a supercharger for compressing air supplied to the engine and thereby boosting intake pressure of air supplied to the engine, and controlling pressure downstream of the supercharger by means of a pressure release valve. Alternatively, the method may include utilizing an E-booster for compressing air supplied to the engine and thereby boosting intake pressure of air supplied to the engine, and controlling pressure downstream of the E-booster by means of a bypass valve. The bypass valve may be closed upon activation of the E-booster and opened upon deactivation of the E-booster. Alternatively, the method may include utilizing a turbocharger for compressing air supplied to the engine and thereby boosting intake pressure of air supplied to the engine. The method may further include controlling operation of the turbocharger by means of an exhaust bypass valve, located downstream of the turbocharger, operable in conjunction with an intake bypass valve, located upstream of the turbocharger.
The method may further include directing exhaust gas from an exhaust heat exchanger to an air compressor via an exhaust gas recirculation (EGR) line, and controlling flow of exhaust gas through the EGR line by means of an EGR control valve.
In another embodiment, the method may include controlling flow of cooled air by means of a throttle, and controlling the mass ratio of air through the throttle by means of a plurality of three-way control valves to thereby control temperature and pressure of air supplied to the engine. Each of the three way control valves may include two input air flow paths and one output air flow path for supplying air to the engine. One of the input air flow paths may receive air controlled by the throttle, the other one of the input air flow paths may receive air from a heat exchanger.
In yet another embodiment, the method may include controlling flow of cooled air by means of a throttle, and controlling the mass ratio of air supplied to at least one of the intake valves by means of at least one variable valve timing device to thereby control temperature and pressure of air supplied to the engine. A first variable valve timing device may control a first intake valve, thereby controlling the supply of air through the throttle tho the first intake valve. A second variable valve timing device may control a second intake valve, thereby controlling the supply of air through a heat exchanger to the second intake valve. Alternatively, the method may include controlling flow of cooled air by means of a throttle, and controlling the mass ratio of air supplied to at least one of the intake valves by means of at least one port throttle to thereby control temperature and pressure of air supplied to the engine. A first port throttle may control flow past a first intake valve, thereby controlling the supply of air through the throttle to the first intake valve. A second port throttle may control flow past a second intake valve, thereby controlling the supply of air through a heat exchanger to the second intake valve.